Electronic telegraph relay

ABSTRACT

1,100,620. Transistor switching circuits. CREED &amp; CO. Ltd. 20 Aug., 1965 [22 Aug., 1964], No. 35917/65. Heading H3T. In an electric pulse relay circuit when the amplitude of the input a exceeds a predetermined level stage 1 is caused to oscillate and when the amplitude of these output oscillations b reach a given value a monostable stage 2, which produces a pulse at c of longer duration than the period of the oscillator, is triggered to control a keying stage 3 arranged to supply D.C. to a load, such as a transistor T3 controlling the connection between telegraph wires 12, 13 for producing a pulse output at d. For an input telegraph signal a (Fig. 3, not shown), as long as the oscillations at b remain above the triggering value for the monostable circuit, pulses at c will continue to be produced until the end of the input signal. The input voltage at which T1 starts oscillating may be varied by resistor R2. A voltage dependent resistor R1 protects the oscillator 1 from overloading and diodes D1, D3 provide bias for transistors T2, T3. In a modified circuit (Fig. 2, not shown) an input signal a causes T1 to oscillate and trigger the monostable stage 2 which then starts to produce an output pulse c. The windings of a common coupling transformer are arranged so that the oscillations of the oscillator 1 are stopped until the end of the output pulse c at (t 4 , Fig. 3, not shown), when oscillations may start again to repeat the above operation. By suitable arrangement of the transformer windings the monostable circuit may either be triggered on the leading or trailing edge of the oscillator pulses. Two relay circuits may be arranged having their input connected in parallel (Fig. 4, not shown), so that input signals of opposite polarity operate one or the other circuit to switch a different pair of telegraph lines for double current working.

Filed March 2, 1965 2 Sheets-Sheet 1 MW M -E:1 e

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Dec. 19, 1967 T. THAULAND 3,359,433

ELECTRONIC TELEGRAPH RELAY Filed March 2, 1965v 2 Sheets -Sheet 2 United States Patent O 1 Claim. of. 307 ss.s

ABSTRACT OF THE DISCLOSURE An electronic telegraph relay is equipped with a constant current generator in its output circuit. As a result, the output current provided by the relay is substantially independent of changes in working voltage and load. Control of the relay is through a single transistor or through two transistors of opposite type which conduct alternately. Constant current output is assured by a constant voltage source including a zener diode placed in parallel with the base-emitter circuit of an output transistor causing the level of conduction of the output transistor to remain steady despite relatively wide variations in working voltage and load.

The present invention relates to electronic telegraph relays and in particular to output relays for telegraph circuits.

It has previously been suggested that a plurality of types of electronic telegraph relays be used to replace electromagnetic relays. Most electronic telegraph relays are designed to have the same ON-OFF action as electromechanical relays. By previously known electronic telegraph relays, faster switching is obtained than by electromechanical relays, but even if the disadvantages of mechanical contacts are avoided, several of the disadvantages of electromechanical telegraph relays are still present.

One of these disadvantages is that most of the previously known electronic telegraph relays are not able to deliver an output current which, within wide limits, is independent of varying working voltage and varying load. The relay only provides for ON and OFF switching of the working voltage and the line current must be adjusted manually each time a chlange is made in the characteristics of the line or of the receiving apparatus together with the ohmic resistance or the circuit will, in many cases, develop in a relatively large time constant, which limits the applicability of the relay.

As mentioned before, the formation of sparks from ma., to receiving apparatus which is designed for 60 ma. As long as the relay is used with particular receiving apparatus, the line characteristics may be varied within wide limits without manual adjustments being necessary. Furthermore, the working voltage source which is used need not be provided with special voltage stabilizing means.

The relay according to the present invention may be used for single current as well as for double current.

An advantage of the invention is that there is obtained a substantial reduction of the time constant L/R, where L is the circuit inductance as represented by the magnet coil of a teleprinter and where R represents the resistance of the circuit against current changes. This resistance R is very large in a constant current generator.

Another feature of the invention is that the constant current generator comprises a transistor which is controlled so that the current through the emitter-collector circuit of the transistor is substantially constant.

In order to perform this control, a reference voltage device is connected between the base electrode of the transistor and the emitter-resistor.

Usually electronic telegraph relays include control circuits which show dependence on incoming control signals which control the ON and OFF switching of one or more transistors, so that the output current at least passes the emitter-collector circuit in one of the transistors.

mechanical contacts is avoided by switching with conventional electronic telegraph relays, but there still arise problems with electromagnetic radiation which in some cases may be very undesirable.

It is a principal object of the present invention to provide electronic relays which provide constant output currents regardless of variations in the supply voltages and in the load.

The main feature of the invention is that at least one constant current generator is used in the output circuit of the relay. When a constant current generator is used in the output circuit of a telegraph relay, the relay will be able to deliver a constant current to the load even if the working voltage for the relay varies and even if the load itself varies.

It will therefore, not be necessary to adjust the output current manually in accordance with varying line and load characteristics. Manual adjustments are only necessary when the type of receiver apparatus is changed, say from receiving apparatus which is designed for 40 Another feature of the invention is that at least one reference voltage device is arranged in or connected to the telegraph relay, so that the potential across the emitter-collector circuit when a transistor is switched ON is compared with the reference potential. Signals resulting from the comparison control the said transistor so that the current through said transistor attains a predetermined substantially constant value which within wide limits is independent of the working voltage and the load.

It is furthermore considered to be advantageous to use a zener diode as reference voltage source.

By using an electronic telegraph relay as defined above, it is possible to obtain a reduced time constant, so that the current reaches the desired level faster and a constant current is obtained for varying working voltage and load. There will, however, always be a risk that if signal pulse edges are too sharp, electromagnetic radiation will result which contains information about the corresponding signal pulse edges, and this should be avoided, in particular, where the relay is used in connection with cryptographic equipment.

According to the present invention a capacitor is, there fore, connected into the output circuit, e.g. from the base electrode to the collector electrode of the output transistor so that there are obtained sof but defined signal transitions.

A further feature of the present invention, when using two constant current generators is that both current generators are arranged to generate constant and equal currents independent of incoming control signals, the two currents in dependence of the control signals, at double current, being alternately applied to the load in opposite directions and at single current, being alternately applied together to and away from the load.

In FIG. 1 an incoming square wave signal is shown connected to -a control circuit SK in the telegraph relay. This control circuit controls a constant current generator KS in such a manner that it, when double current is used, is

connected to plus (-1-) in one case and minus in the other case, and when single current is used, alternately is connected to one of the battery terminals and to no battery terminal. The constant current generator KS is, therefore, always connected into the circuit when current is applied to the load Z.

In FIG. 2 is shown a principal diagram of another embodiment of the invention where two constant current generators KS1 and KS2 are used. KS1 is in this case connected to plus, While KS2 is connected to minus. The square wave signals applied to the control circuit SK provides switching of the constant current generators KS1 and KS2 so that only one of these at any time is connected into the output circuit of the relay. This embodiment of the invention is particularly suitable for transmitting double current signals.

In FIG. 3 the control signal, i.e. the square wave signal is shown connected to the base electrodes of two transistors, TR1 and TR2, via a voltage divider, R1 and R2. These transistors are controlled OFF and ON so that only one is conducting at a time. When therefore, the transistor TR1 is switched ON, the transistor TR2 is automatically switched OFF. Furthermore the transistor TR3 will be switched OFF when the transistor TR1 is switched OFF and vice versa, as the emitter-collector-circuit for the transistor TR1 is connected in series with the resistors R3 and R4 between the battery terminals zero and minus for controlling the transistor TR3. Correspondingly the transistor TR4 will be switched off when the transistor TR2 is switched off and vice versa, as the emitter-collector circuit for the transistor TR2 is connected in series with the resistors R5 and R6 between the battery terminals zero and plus, for controlling the transistor TR4. When the transistor TRS is switched OFF, the transistor TRS will be switched ON, but when the transistor TR3 is switched ON, the transistor TR5 will be switched OFF due to the negative potential which is applied to the base electrode of this transistor from minus via TR3 and the resistor R7. The transistor TR6 will correspondingly be switched ON when the transistor TR4 is switched OFF, but the transistor TR6 will be switched OFF when the transistor TR4 is switched ON, due to the positive potential which is applied to the base electrode of the transistor TR6 from plus via R and transistor TR4. From plus to minus there is in series with a resistor R11 connected two zener diodes Z1 and Z2. When transistor TR3 is switched OFF, and the transistor TR4 is switched ON as mentioned above, a current flows from plus through the resistance RIO-the emitter-collector circuit for the transistor TR4-R11-Z1 to minus. As previously stated the transistor TRS is switched ON when the transistor TR3 is switched OFF, so that the potential across the resistors R7, R8 and the emitter-base-circuit for the transistor TRS is determined by the potential across the zenerdiode Z1. The relation between the breakdown potential of the zener-diode and the resistors R7 and R8 is determined so that there will flow a predetermined substantially constant current in the emitter-collector'circuit of the transistor TRS and, therefore, also through the load Z.

correspondingly there will flow a current from plus through resistors R10, R9, transistor TR6 and load Z to zero, when the transistors TR3 and TR4 respectively are controlled ON and OFF. The circuits which respectively comprise resistors R7, R8 and transistor TR5, and resistors R10, R9 and transistor TR6, provide together with the zener-diodes Z1 and Z2 and the resistor R11 two constant current generators. If the working voltage source positively is very stable, the zener-diodes Z1 and Z2 may be exchanged with resistors.

As will be seen from the figure, a capacitor C1, C2 is connected across the base-collector circuit for each of the output transistors TRS and TR6, in order to obtain soft signal transitions.

The circuit which is shown in FIG. 3 may also be used for single current, by only using one half of the circuit.

One end of the resistor R11 must then, however, be connected to zero. If e.g. the upper half of the circuit is to be used, the lower end of resistor R11 must be connected to zero. This circuit is within wide limits independent of variations in the working potential. If e.g. normal battery potentials are :35 v., the circuit will work satisfactorily even at battery potentials of :20 v. and :50 v. The circuit is furthermore substantially independent of the load Z. If the load Z represents the magnet coil in a teleprinter, a plurality of such magnet coils, i.e. teleprinters, may be connected in series.

In FIG. 4 is shown a circuit which is particularly designed for transmission of single current signals. In this circuit is furthermore used two output transistors connected in series, TR10 and TR9, so that the circuit may be connected to a relatively large voltage source, without using special transistors. The controlling square wave signals control the transistor TR7 via the voltage divider R12 and R13. When the transistor TR7 is switched OFF, transistor TR8 will also be switched OFF as the emittercollector circuit for TR7 is connected in series with the resistors R14 and R15 between the battery terminals zero and minus for controlling the transistor TR8. When the transistor TR8 is switched OFF, the transistor TR9 will be switched ON due to the positive potential which is supplied to the base electrode of transistor TR9 from zero, via the resistors R16 and R17. A diode D1 is arranged for providing the necessary bias for transistor TR9. TR9 acts in this case as a switch for TRIO and also for the output current. When, therefore, TR9 is switched ON, a current fiows from zero through the load Z, further through the emitter-collector circuit for transistor TRIO-resistor R18collector-emitter circuit for transistor TR9 and diode D1 to minus. There will furthermore flow a current fro mzero through resistor R19 and zener-diode Z3, transistor TR9, diode D1 to minus, so that the potential across R18 in series with the emitterbase-circuit for transistor TRIO solely is controlled by the potential across the zener-diode Z3. The current flowing through the transistor TR10 is, therefore, predetermined by the components R18 and Z3 so that there will flow a substantially constant current through this transistor and through the load Z. When, however, the transtistor TR9 is switched OFF, there will not flow any current through either the load Z, transistor TR10' or through the zener-diode Z3. In order to obtain soft signal transistions, a capacitor C3 is in this circuit connected from the base electrode of the first output transistor TR9 to the collector electrode for the other output transistor TRIO.

In FIG. 5 is shown a circuit for an electronic telegraph relay according to the present invention which may be used for single current as well as for double current by setting a switch S2 to the one or the other of its two positions. In this circuit there is included a switch S1 which connects a resistor R25 into the circuit or short circuits this resistor in a simple manner to enable the adjustment of a telegraph relay to one of two current levels. It may e.g. in some cases be desirable to use 40 ma. In this circuit the transistors TR14 and TR15 are controlled by selecting the values of the components Z4 and R2 3-R25, so that there always flows a current of equal magnitude through the respective emitter-collector circuits. It is in the following assumed that the components are chosen so that there always will flow 20* ma. through transistor TR15 and 20 ma. through transistor TR14. It is furthermore assumed that it is desirable to send double current. The incoming square wave signal is supplied to the base electrode of transistor TR11, so that the transistors TRIZ and TR13 automatically are switched OFF and ON. When the transistor TR1? therefore is switched ON there will flow 40 ma. through this transistor, as 20 ma. flows through TR15 and further through TR13, while 20 ma. flows through TR14, further through the load Z, as the transistor TR12 is blocked, and through the transistor TR13 to the negative battery terminal. When correspondingly the transistor TR12 is switched ON while the transistor TR13 is switched OFF, the current through transistor TR14 flows right through transistor TR12 and diode D2 to minus, while the current through transistor TRIS in this case will flow through the load Z in opposite direction and further through transistor TR12 and diode D2 to minus.

The resistor R20 is arranged to provide the necessary bias for transistor TR11 and resistor R21 is connected to the collector-electrode of the transistor in order to complete the circuit.

If, however, it is desirable to send single current signals, the switch S2 is switched to its other position, so that the current through the transistor TR14 and the transistor TRIS flows together, in one case right through the transistor TR14 to minus, and inthe other case through the load Z and through transistor TR12 and the diode D2 to minus.

In order to obtain soft signal transistions there are connected capacitors C4 and C5 across the base-collector circuit for transistors TR12 and TR13 respectively.

It should be noted that the above detailed description of several embodiments of the invention in no manner must be considered as limiting for the scope of protection.

What is claimed is:

An electronic telegraph relay including control circuits and a pair of constant current generators responsive to input pulses of positive and negative polarity for providing distinct output currents of positive and negative polarities at amplitudes which are substantially independent of changes in working voltage and independent of changes in load, comprising:

(1) a first control circuit including a first PNP transistor coupled to a first NPN transistor, each having a base, an emitter, and a collector,

an input terminal connected to the base of the first PNP transistor, means biasing the first PNP transistor to a state of conduction in response to negative input pulses on the input terminal, means biasing the first NPN transistor to a state of conduction in response to conduction in the collector of the first PNP transistor,

(2) a second control circuit including a second NPN transistor coupled to a second PNP transistor, each having a base, an emitter and a collector,

means connecting the base of the second NPN transistor to the input terminal, means biasing the second NPN transistor to a state of conduction in response to positive input pulses on said terminal,

means biasing the second PNP transistor to a state of conduction in response to conduction in the collector of the second NPN transistor,

(3) a first constant current generator including a third NPN transistor having a base serving as the generator input terminal, an emitter, and a collector,

a zener diode connected between the emitter and the base of the third NPN transistor to assure constant current output,

means coupling the input terminal of said first constant current generator tosaid first NPN transistor and for biasing said generator into conduction to deliver a negative output current when said first NPN transistor is non-conducting and biasing the generator to a non-conductive state when said first NPN transistor is conducting,

(4) -a second constant current generator including a third PNP transistor having a base serving as the generator input terminal, an emitter and a collector,

a zener diode connected between the emitter and the base of the third NPN transistor to assure constant current output,

means coupling the input terminal of said second constant current generator to said second PNP transistor and for biasing said generator into conduction to deliver a positive output current when said second PNP transistor is non-conducting and biasing the generator to a non-conducting state when said second PNP transistor is conducting, and

means connected to the collector of the third PNP transistor and to the collector of the third NPN transistor to deliver the respective positive and negative output currents at a common terminal.

References Cited UNITED STATES PATENTS 2,602,151 7/1952 Carbrey 328-483 3,114,872 12/ 1963 Allard 307-88.5 3,125,694 3/1964 Palthe 30788.5 3,150,272 9/1964 Gard 307-88.5 3,189,758 6/1965 Bell 30788.5 3,191,121 6/1965 Nelson 307-88.5 X 3,247,494 4/1966 Ashley 340-174 ARTHUR GAUSS, Primary Examiner.

I. ZAZWORSKY, Assistant Examiner. 

